1. Field of the Invention
The present invention relates to bow sights, and in particular to bow sights for use both on level ground and elevated stand applications. The present invention includes both sighting and range-finding capability.
2. Prior Art
Archery, especially in hunting, involves shooting from a level ground position to a target on either level or sloping terrain. In addition, shooting from tree stands of various heights is also common. Bow sights are calibrated by setting up a target of a given height and at a measured distance, usually twenty yards, through which the arrow will have a flat trajectory. The bow sight is calibrated by aligning a sight on the bow string with a movable shooting pin positioned on a frame attached t the bow. The shooting pin is fixed into position at a point where a fired arrow strikes the target. The shooting pin is now fixed at a twenty yard range and the bow is calibrated for that range. Fixed pins for greater distances are often used and are positioned vertically below the flat trajectory pin. As the bow is tilted upwardly to bring one of these lower fixed pins in alignment with the target and the bow string sight, the bow sight can be calibrated by trial-and-error for these greater distances.
Pendulum sights have been developed for use with sighting pins to provide for bow sight calibration at distances greater than the flat-trajectory range. In U.S. Pat. No. 4,580,349 (Webb et al.) a pendulum is attached to a bow frame and provides a means by which a range mark can be recorded to mark the position of the pendulum at the longer calibrated distances. When the pendulum is aligned with a previously established range mark, the bow will be tilted at the correct angle for use with a given sighting pin. A plurality of sighting pins are used, each for a particular range.
When hunting from an elevated tree stand, the bow is initially calibrated for a flat trajectory range, such as twenty yards, as measured from a point below the tree stand and the target. Pendulum sighting devices are also used in the application. These devices work on the principle that relative movement of a pin mounted on the pendulum is different than that of the fixed pin with respect to the bow string sight when the bow is raised or lowered in angle from a tree stand position. The pendulum is moved up or down the bow frame until the arrow strikes the target when the pendulum pin is on the target. Once locked into position, the pendulum is calibrated for only that specific tree stand height. If the archer were to move to a tree stand having higher elevation and aim at the same target used in calibration, the greater downward angle of the bow will cause greater relative movement of the pendulum and indicate that the target is further away than it actually is. The inaccurate distance reading results from the increased elevation with respect to the elevation at which the bow sight was calibrated. This increase in elevation causes the pendulum pin to move upwardly with respect to the line-of-sight through the bow string sight initially established. Devices in the prior art would have to be recalibrated by lowering the pendulum mounting frame to place the pendulum pin in alignment with the target. See U.S. Pat. Nos. 4,120,096; 4,368,581; and 4,616,422. These devices acknowledge the limitations of the respective disclosed sighting apparatus and simply assume that, since most hunting distances are at ranges of less than thirty yards, any inaccuracies that arise due to elevation changes are not important. In short, prior art pendulum devices assume a given tree stand height range of ten to thirty feet or so and a usable range of less than thirty yards. The resulting inaccuracies are ignored.
The principles involved in changed elevation are also applicable to pendulum devices used in situations where the terrain itself may be sloping upwardly or downwardly. The pendulum pin should be at the same point above a line-of-sight from a fixed shooting pin through the bow string sight for the same range greater than the flat trajectory range regardless of elevation. To put it another way, the line-of-sight through the pendulum pin should be in the same angular position with respect to the arrow for the same range regardless of elevation. The arrow always remains at 90.degree. with respect to the bow. The prior art devices lack the capability t alter the relative movement of the pendulum pin as elevation changes and accordingly, these devices are only accurate at the height at which they were calibrated.
What is desired in a bow sighting device is a pendulum sight wherein the relative angular movement of the movable pendulum pin can be modified depending upon the elevation at which it is used. Such a sighting device would also have range indicating capability when properly calibrated.